758 research outputs found
Cooperative Beamforming for Wireless Ad Hoc Networks
Via collaborative beamforming, nodes in a wireless network are able to
transmit a common message over long distances in an energy efficient fashion.
However, the process of making available the same message to all collaborating
nodes introduces delays. In this paper, a MAC-PHY cross-layer scheme is
proposed that enables collaborative beamforming at significantly reduced
collaboration overhead. It consists of two phases. In the first phase, nodes
transmit locally in a random access time-slotted fashion. Simultaneous
transmissions from multiple source nodes are viewed as linear mixtures of all
transmitted packets. In the second phase, a set of collaborating nodes, acting
as a distributed antenna system, beamform the received analog waveform to one
or more faraway destinations. This step requires multiplication of the received
analog waveform by a complex weight, which is independently computed by each
cooperating node, and which allows packets bound to the same destination to add
coherently at the destination node. Assuming that each node has access to
location information, the proposed scheme can achieve high throughput, which in
certain cases exceeds one. An analysis of the symbol error probability
corresponding to the proposed scheme is provided.Comment: 5 pages, 4 figures. To appear in the Proceedings of the IEEE Global
Communications Conference (GLOBECOM), Washington, DC, November 26 - 30, 200
Homoclinic solutions for a class of asymptotically autonomous Hamiltonian systems with indefinite sign nonlinearities
In this paper, we obtain the multiplicity of homoclinic solutions for a class of asymptotically autonomous Hamiltonian systems with indefinite sign potentials. The concentration-compactness principle is applied to show the compactness. As a byproduct, we obtain the uniqueness of the positive ground state solution for a class of autonomous Hamiltonian systems and the best constant for Sobolev inequality which are of independent interests
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